The present invention relates to a photopolymerizable mixture comprising a polymeric binder, a polymerizable compound having at least two acrylate or alkacrylate groups in the molecule, and a photoinitiator combination.
Photopolymerizable mixtures containing acrylates and/or methacrylates as photopolymerizable compounds are known. For the production of photoresist materials, in particular dry photoresist layers, mixtures are preferred containing acrylates or methacrylates having urethane groups in the molecule that can be developed using aqueous alkaline solutions. Such mixtures are described,. for example, in U.S. Pat. Nos 3,782,961; 3,850,770; 3,960,572; 4,019,972 and 4,250,248.
Photopolymerizable mixtures are also known which, in order to increase the photosensitivity, contain certain combinations of photoinitiators and activators, for example combinations of carbonyl-group-containing initiators and tertiary amines. Such mixtures with a synergistic action are described, for example, in U.S. Pat. Nos. 4,054,682; 4,071,424 and 3,759,807. A disadvantage of these mixtures containing low-molecular-weight amines is that they have a short shelf life since the amines can easily bleed out, in particular from thin coatings.
In JP-A No. 50/129,214, filed on 2 Apr. 1974 with number 49/36,614, a photopolymerizable mixture is described containing a tetra(meth)acrylate of a N,N,N',N'-tetrahydroxyalkyl-alkylenediamine as the polymerizable compound. The tetrafunctional compound serves as a crosslinking agent.
It is also known that the free-radical polymerization of ethylenically unsaturated compounds can be initiated by irradiation with visible light in the presence of photoreducible dyes and reducing agents, for example amines (U.S. Pat. No. 3,097,096). However, these initiator combination are essentially employed only in aqueous solution or in combination with water-soluble binders.
Initiator combinations of photoreducible dyes and other reducing agents are described in U.S. Pat. Nos. 3,597,343 and 3,488,269. Photopolymerizable mixtures containing exclusively photoreducible dyes as initiators have hitherto not been employed in practice due to their unsatisfactory photosensitivity.
In JP-A No. 54/151,024, a photopolymerizable mixture is described containing an initiator combination of a merocyanine dye and a trihalomethyl-substituted s-triazine that is sensitive towards visible light, for example an argon laser. However, the sensitivity of these mixtures towards visible laser light is inadequate for practical use.
German Patent Application No. P 37 10 281.8 describes photopolymerizable mixtures containing (meth)acrylates having urethane groups, tertiary amino groups and optionally urea groups in their molecules; polymeric binders; and, as photoinitiators, a combination of a photoreducible dye, a radiation-sensitive trihalomethyl compound and an acridine, phenazine or quinoxaline compound.